SWITCH BOARDS AND MAIN
TRANSFORMER
There are two switch boards in the Power Wave 455M
machine. Each contains an input capacitor and insu-
lated gate bipolar transistor (IGBT) switching circuitry.
Refer to Figure E.3. When the machine reconnect
switches are configured for a lower input voltage
(below 300VAC), the input capacitors are connected in
parallel. When the machine is configured for higher
input voltages (300VAC and above), the input capaci-
tors are connected in series.
When the input capacitors are fully charged, they act
as power supplies for the IGBT switching circuits. The
insulated gate bipolar transistors switch the DC power
from the input capacitors "on and off," thus supplying
pulsed DC current to the main transformer primary
windings. See IGBT OPERATION DISCUSSION AND
DIAGRAMS in this section.
Each switch board feeds current to a separate, oppo-
sitely wound primary winding in the Main Transformer.
The reverse directions of current flow through the main
transformer primaries, and the offset timing of the IGBT
switch boards induce an AC square wave output signal
at the secondary of the main transformer. Current
transformers located on the switch boards monitor the
primary currents. If the primary currents become
abnormally high, the Control Board will shut off the
IGBTs, thus disabling the machine’s output. The firing
of the two switch boards occurs during halves of a 50-
microsecond interval, creating a constant 20 KHZ out-
put.
E-4 E-4
THEORY OF OPERATION
POWER WAVE 455M/MSTT
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NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.
FIGURE E.3 - SWITCH BOARDS AND MAIN TRANSFORMER
